During the construction of underground wells, it is common, during and after drilling, to place a liner or casing, secured by cement pumped into the annulus around the outside of the liner. The cement serves to support the liner and to provide isolation of the various fluid-producing zones through which the well passes. This later function is important since it prevents fluids from different layers contaminating each other. For example, the cement prevents formation fluids from entering the water table and polluting drinking water, or prevents water from passing into the well instead of oil or gas.
A problem which is encountered in the placement of cement in wells is the development of gel strength in situations in which materials are easily lost from the cement slurry before it is set in the correct position. One example of this is in the placement of cement for lost circulation problems. In normal cement systems, the cement is pumped into the well in a slurry that is very fluid and gel strength develops during the early part of the setting reaction. However, this can take a significant time during which some or all of the components of the cement slurry can be lost to the formation. It has been proposed to add fibers to cement slurries to help build a filter cake and retain the cement in position. However, the lack of a gel structure still makes loss of materials to the formation a problem.
It is an objective of the present invention to provide well cementing systems that can be placed by pumping in the normal manner, and which contain materials that favor the development of the gel strength for curing lost circulation.